Recently, an apparatus using a microwave has been proposed as an apparatus for performing a heat treatment on a substrate such as a semiconductor wafer. The heat treatment using a microwave is known to have a great process advantage, as compared with a conventional annealing apparatus using lamp or resistance heating, in that internal heating, local heating, and selective heating can be achieved. For example, when the microwave heating is used to activate doping atoms, there are advantages in that excessive heating does not occur and a diffusion layer can be restrained from expanding because the microwave directly acts on the doping atoms. In addition, the heating using microwave irradiation advantageously allows an annealing process at a relatively low temperature and thus restrains thermal budget from being increased as compared with the conventional lamp or resistance heating manner. However, since a microwave has a long wavelength of several tens of millimeters and further has characteristics of easily forming a standing wave in a processing vessel, a distribution of strong and weak electromagnetic fields may be generated in a substrate plane and non-uniformity of heating temperature may thus occur in some cases. Therefore, it is difficult to control a temperature of the entire substrate only by using an output of the microwave, and thus, in order to prevent the occurrence of an excessive temperature distribution, an annealing process considering a balance between cooling and heating by using the microwave is considered as being necessary.
In order to cool the substrate, which is being heated or has been heated by microwave irradiation, in the processing vessel of the microwave heat treatment apparatus, a gas cooling method in which a cooling gas is introduced into the processing vessel may be contemplated. For example, there has been proposed a heat treatment apparatus, in which a flow rate of air injected from an injection plate installed in a lower portion of a processing vessel is changed for each of a plurality of regions to improve uniformity of an in-plane temperature distribution of the substrate. In addition, although a temperature control of a substrate is not an objective, there has been proposed a vapor deposition apparatus configured to independently control an amount of a purge gas injected from a shower head, which is installed in an upper portion of a processing vessel facing the substrate, for each of a plurality of regions.